The recognition of fingerprints is commonly used to identity a person through his fingerprints.
A database of fingerprints generally catalogs a multitude of fingerprint images with a set of characteristic points for each one and a match with an identity of someone to whom the fingerprint is attributed.
A fingerprint image consists of a certain number of relatively dark lines separated by relatively light lines with stopping points and points of modification of curvature that constitute the characteristic points of the fingerprint.
To establish a one-to-one match between an image that results from the taking of a print of unknown identity and an image of a print from the database, one proceeds overall in the following manner. The unknown print image is presented to a specialist who determines characteristic points of the unknown print. The unknown print image together with its determined characteristic points, is submitted to a computer system which compares it with the images of the database. The computer system picks out from the images of the database, a sample of those that an algorithm judges in a known manner, to be the closest to the image submitted. The images picked out by the computer system are thereafter presented to the specialist who compares them with the unknown print image so as to find a match between the unknown print image and a print image from the database.
A problem arises when the unknown identity of the print results from having taken it from some arbitrary surface, in particular a non-planar surface. This is the case, for example, in a police inquiry during which fingerprints are taken from any type of object. The results are not always as accurate as for fingerprints that result from the even pressure of a finger on a planar surface specifically provided for this purpose. In particular, certain lines may be distorted, on account for example, of local deformation of the skin due to its elasticity or of a distortion of the supporting object while the print is being deposited.
To determine the characteristic points before submission to the computer system, the specialist is confronted with an effort of imagination that is continuously sustained during the observation of the image to interpret whether, for example, a break in line curvature gives rise to a characteristic point determination or whether it seems rather to result from a fault with the taking of the print by comparison with the whole image.
When several fingerprint images, picked out by the computer system as having characteristic points of the fingerprint of unknown identity, are presented to the specialist so that he may choose the one he judges to be closest to the image under study, the specialist is again confronted with an effort of imagination in order to compare each image presented with the image submitted. On account of absence of similarity that results from faults with the taking of prints, the specialist must raise the matter of ascertaining for each image presented whether an absence of similarity results from the fact that the fingerprint is different or from the fact that the print taken is spoilt. This additional intellectual effort impedes efficiency and induces fatigue in the specialist.